如何使用IF和ELSE語句進行sql查詢

我有查詢來選擇獲取答案值。我需要檢查它是否應答或爲空。我用（d.AM_Answer或null）它不起作用。它只取空值。所以，我改變了我的下面的查詢，但它不工作。如何使用IF和ELSE語句進行sql查詢

SELECT a.QM_ID, 
     a.QM_QCM_ID, 
     a.QM_Question, 
     a.QM_Type, 
     a.QM_Parent_Id, 
     c.AM_Answer, 
     c.AM_Comments 
FROM question_master a 
INNER JOIN Assessment_master c ON (c.AM_QM_ID = a.QM_ID 
            AND c.AM_HNM_ID = %d 
            AND c.AM_HM_ID = %d 
            AND c.AM_ASM_Local_Id = %@) 
WHERE a.QM_Parent_Id = 0 
    AND a.QM_Status = 'A' 
    AND a.QM_QCM_ID = %@ 
    AND a.QM_QRM_Id = %@ IF(d.AM_Answer IS NULL) THEN 
UNION 
SELECT b.QM_ID, 
     b.QM_QCM_ID, 
     b.QM_Question, 
     b.QM_Type, 
     b.QM_Parent_Id, 
     NULL, 
     NULL 
FROM question_master b 
INNER JOIN Assessment_master d ON ((d.AM_QM_ID = b.QM_Parent_Id 
            OR d.AM_QM_ID = b.QM_ID) 
            AND d.AM_HNM_ID = %d 
            AND d.AM_HM_ID = %d 
            AND d.AM_ASM_Local_Id = %@) 
WHERE b.QM_Parent_Id != 0 
    AND b.QM_Status = 'A' 
    AND b.QM_QCM_ID = %@ 
    AND b.QM_QRM_Id = %@ ELSE IF(d.AM_Answer IS NOT NULL) THEN 
UNION 
SELECT b.QM_ID, 
     b.QM_QCM_ID, 
     b.QM_Question, 
     b.QM_Type, 
     b.QM_Parent_Id, 
     d.AM_Answer, 
     d.AM_Comments 
FROM question_master b 
INNER JOIN Assessment_master d ON ((d.AM_QM_ID = b.QM_Parent_Id 
            OR d.AM_QM_ID = b.QM_ID) 
            AND d.AM_HNM_ID = %d 
            AND d.AM_HM_ID = %d 
            AND d.AM_ASM_Local_Id = %@) 
WHERE b.QM_Parent_Id != 0 
    AND b.QM_Status = 'A' 
    AND b.QM_QCM_ID = %@ 
    AND b.QM_QRM_Id = %@ END IF

來源

2014-02-27 user3351727

從http://dev.mysql.com/doc/refman/5.7/en/working-with-null.html：不能使用算術比較運算符（如=，<, or <>）來測試NULL。 – mcalex

@mcalex他可以使用IS NULL –

我猜它知道goves你的錯誤，因爲聯合關鍵字 –

1）要檢查空值，可以使用COALESCE運算符。

2）您也可以使用SQL CASE語句

3）我建議你爲你準備一個動態查詢

來源

2014-02-27 05:42:31

哪裏可以更改我的代碼 – user3351727

您可以在查詢中說明每個聯合的目的嗎？ –

使用存儲過程，這個你可以把這裏的條件d.answer是不爲null以選擇非空答案。

來源

2014-02-27 05:44:13 Cerberus

嘗試

IF(d.AM_Answer IS null)

，而不是

IF(d.AM_Answer == null)

來源

2014-02-27 05:47:06 Prashant16

如何使用IF和ELSE語句進行sql查詢

回答

相關問題